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Abstract To study the mechanical behavior of salt rock under cyclic loading，the uniaxial compression tests were conducted with thenardite，bedded thenardite and rock salt specimens respectively. It is demonstrated that the strength of thenardite under cyclic loading is lower than that under monotonic loading. The strength of bedded thenardite with calcium mudstone is higher than that of pure thenardite. However，the strain at the point of peak strength is less than that of the later because of the hard interlayer effect. Different from other rocks，at the initial period，the loading and unloading curves almost overlap each other. With the development of loading stress and cyclic time，the phenomenon of the plastic hysteresis loop during unloading period occurs slightly，but the loop area is small. During the later period，the Young′s modulus in the unloading process is larger than that in the loading process to certain extent due to the slight plastic hysteresis. For the bedded thenardite，the Young′s modulus is larger than that of pure thenardite because of the effect of the hard interlayer. Simultaneously，it is found that the recovery of plastic deformation of the bedded thenardite is larger than that of pure salt rock during the unloading process. The Young′s modulus of salt rock，on the whole，is almost consistent during the cyclic loading even with slight plastic recovery hysteresis at the later period with stress and cyclic number development. The common phenomenon of Young′s Modulus decreasing with yield stress in yielding and damaging periods for general rock material does not happen for salt rock. From the point of energy theory view，the strength decrease magnitude of rock during cyclic loading is relative to cyclic time and accumulated area of the hysteresis loop. In the tests，the loading and unloading curves are almost overlapped and the hysteresis loops are small，therefore the strength decrease magnitude is also less. Consequently，it could be deduced that the strength of the surrounding salt rock in a salt cavern storage will be less affected by cyclic injection and withdraw. However，strong pressure fluctuation could make energy accumulated in rock mass，thus the strength and longevity of the cavern are inevitably harmed.
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Received: 14 May 2010
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2011, Vol. 30 
